Antibiotic A23187 is a pyrrole polyether ionophore produced by Streptomyces chartreusis. The predominate mechanism by which this compound initiates a kaleidoscope of biological responses appears to be through its ability to selectively transport ions of physiological importance across cell membranes. The A23187:Me plus 2 complex has been studied in organic solvent systems, but the structure of the complex and the transport process in organic solvents does not appear to be the same as that observed in artificial and natural membrane systems. Upon completion of biosynthetic studies with the A23187 producing strain of S. chartreusis, specifically and highly enriched C-13 labeled antibiotic will be available to examine the interaction of this compound with lipids in organic solvents and in artificial membrane systems. In this study, C-13 enriched A23187 will be examined by C-14 NMR in the presence of different lipids and in lipid vesicles. The C-13 NMR chemical shifts and spin lattice relaxation times of the enriched carbons will indicate which parts of the molecule have the strongest interaction with the lipid. Radio- and stable-isotope labeled A23187 will also be used to examine how this compound transports small molecular weight amino acids into organic solvents and how it inhibits protein synthesis in cell free systems. It is essential that the biosynthetic labeling pattern for A23187 be established prior to examining its mechanism of action. A series of biosynthetic feeding experiments using C-14, N-15 and C-13 labeled precursors will be carried out to establish this pattern.